There are a variety of methods for transmitting information via a broadband Integrated Services Digital Network (B-ISDN), using a variety of protocols related to Asynchronous Transport Mode (ATM), frame relay mode, ISDN and SS#7 modes, and Internet-mode of transmission. Each of these modes permit the transmission of an original stream of information by time-dividing it into a plurality of discrete cells or packets. As used in the field, packets may have a variable size but cells typically have a predetermined size, such as the 53-byte sized ATM cell. The ATM mode, as the exemplary preferred embodiment, was originally investigated by a group called the International Telephone and Telegraph Consultative Committee (CCITT). The group, currently called the International Telecommunication Union-Telecommunications Standards Sector (ITU-TSS), investigated a new form of ISDN that would have the flexibility to accommodate a large number of channels and the ability to transfer large amounts of data at a very fast rate. At the end of the study, the committee decided to adopt ATM as the target transfer mode for the B-ISDN. The ITU-TSS is currently defining the wide area network (WAN) standards for ATM.
ATM is a transfer mode that sends 53 octet packets (since the size is fixed, they also are considered as cells) of information across a network from one communication device to another. The 53 octets are comprised of 48 octets of data information, referred to as the payload, and 5 octets of header information (including the routing information). The header and data information must be organized into cells so that when the cells are filled, they can be sent when an open slot of 53 octets becomes available.
Although ATM based transmission, switching, and network technology has been employed in broadband integrated services digital networks (B-ISDN) which rely on fiber optics, there are numerous difficulties associated with implementing ATM based technology in a wireless communication network. Similar difficulties are found in other cell- or packet-based systems, such as frame relay, Internet, ISDN and SS#7 systems. These difficulties include the fact that cell or packet-based networks and switches rely on a number of high speed interfaces. These high-speed standard interfaces include OC-3 (155 Mbit/s), OC-12 (622 Mbit/s) and DS3 (45 Mbit/s). However, few cell- or packet-based networks and switches support lower speed interfaces, such as T1 (1.544 Mbit/s) and the programmable rate RS-449 interface.
As a consequence, there are only a few interfaces which can support the comparatively low transmission rates (less than 1 Mbit/s to a 8 Mbit/s) used in wireless communication. Although commercial satellite and wireless modems support these low transmission rates using an RS-449 programmable rate interface, it is difficult to implement cell- or packet-based technology in a wireless environment using conventional interfaces because most ATM traffic is transmitted over high rate data interfaces.
Another difficulty associated with implementing cell- or packet-based technology in a wireless communication network has to do with the fact that cell- or packet-based protocols rely on extremely low bit error ratios which are typical of fiber optics based networks. By way of example, ATM protocols assume that the transmission medium has very low Bit Error Ratios (BER) (10−12) and that bit errors occur randomly.
In contrast, the bit error ratios associated with wireless communication are much higher (on the order of 10−3 to 10−8) and tend to fluctuate in accordance with atmospheric conditions. In addition, the errors associated with wireless communication tend to occur in longer bursts. Thus, a robust error correction scheme must be employed in a wireless network in which cell- or packet-based technology is to be implemented.
In addition to the difficulties discussed above, there is another significant constraint placed on wireless communication networks which is not imposed on terrestrial based fiber optics networks. This constraint has to do with the fact that the cost of bandwidth in a wireless network is much higher than for fiber optics networks. As a consequence of having been traditionally implemented in fiber optics networks, ATM-based technology is not particularly efficient in its use of transmission bandwidth. Therefore, if ATM-based technology is to be implemented in wireless networks, it must achieve a more efficient use of bandwidth. These same goals apply to ISDN/SS#7 and Internet transmissions, and those generally using TCP/IP protocols. However, no solution to problems blocking achievement of these goals is seen in the prior art.
For example, U.S. Pat. No. 5,568,482 relates to a low speed radio link system and method designed for ATM transport. The system is based on a data protocol which is compatible with non-wireless ATM based data transmission systems. The data protocol incorporates a frame format which allows for the transmission of ATM cells in low speed, high noise links. However, the data protocol is rigid and does not account for partial or compressed cells. Similarly, the reference fails to accommodate flexible data payloads or flexible block codes for error correction.